Macrocyclic polyethers in which four to approximately twenty oxygen atoms are separated from one another each by two or more carbon atoms have in recent years aroused considerable interest in many fields of chemistry. They form stable complexes with alkali- and alkaline earth cations, in which the cation is surrounded by the oxygen atoms of the polyether macrocycle.
Through the formation of complexes with macrocyclic polyethers, inorganic salts can be made soluble in organic solvents in which they are normally virtually insoluble in the absence of the cyclic polyether. Organic salts complexed with cyclic polyethers--alkali picrates for example--can be extracted with organic solvents from aqueous solutions (see for example C. J. Pedersen and H. K. Frensdorff, Angew. Chem. 84, 16 (1972)). For example, even potassium permanganate or potassium tert.-butanolate dissolve in aromatic solvents if macrocyclic polyethers of suitable magnitude are added. Furthermore, the complexation of the cation greatly increases the dissociation of the ion pair between cation and anion. It is thus possible to increase the conductivity of salt solutions in organic solvents. Through the complexation of the cation and the shielding of the charge, highly reactive "naked" anions are formed, i.e., anions which are weakly or not at all complexed, and which are being used increasingly for substitution reactions.
It is assumed that the special effect of the cyclic polyethers is based on the fact that the cation is received into a polar, hydrophilic cavity of the ether molecule, while the exterior of the molecule is lipophilic. This effect is limited to cyclic compounds, and is known as the macrocyclic effect (B. Dietrich, J.-M. Lehn and J. P. Sauvage, Chemie in unserer Zeit 7, 120 (1973)). It is in harmony with this that, in comparative experiments with the open-chain oligoethers diglyme (CH.sub.3 OCH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 OCH.sub.3) and triglyme (CH.sub.3 OCH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 OCH.sub.3), the alkali picrate extraction from aqueous phase by means of an organic solvent cannot be performed. (F. Vogtle and E. Weber, Angew. Chem. 86, 896 (1974), W. Wehner and F. Vogtle, Chem. Exp. Didakt. 1, 77 (1975)).